Compact discs (CDs), recordable compact discs (CD-Rs), rewritable compact discs (CD-RWs), digital versatile discs (DVDs) or recordable DVDs that offer higher density and the like are conventionally known as optical recording media. In an optical pickup for recording and playback these recording media, a compact semiconductor laser device is conventionally used as a light source.
There are two types of generally known semiconductor laser devices: a semiconductor laser device using a can package and a semiconductor laser device using a frame package. In the semiconductor laser device using a can package, leads are individually attached to a metal stem, and a laser element placed on the metal stem is sealed with a cap. In the semiconductor laser device using a frame package, a metal frame on which a semiconductor laser element is placed is formed by insert molding by using resin. The semiconductor laser device using a frame package can be mass-produced, and thus can be produced at lower cost. It is for this reason that the semiconductor laser device using a frame package has been receiving increasing attention.
However, the semiconductor laser devices using a frame package offer lower thermal dissipation than the widely-used semiconductor laser devices using a can package, and therefore often find application in infrared laser devices having stable temperature characteristics. Thus, further improvements have been sought therein so as to make them usable in high output power laser devices for CD-Rs or CD-RWs, red laser devices for DVDs or the like, dual wavelength laser devices, or blue laser devices that operate at high voltage.
A semiconductor laser device using a frame package that can solve the problem described above is disclosed in Patent Publication 1. This semiconductor laser device has a structure in which a portion of a frame on which a semiconductor laser element is placed is made thicker and is exposed on a bottom face thereof. However, in order to make the thick portion of the frame protrude through a resin member on the back face thereof in a manner as described above, it is necessary to reduce the thickness of the resin member disposed on the back face of the frame so as not to prevent protrusion of the thick portion of the frame. This makes it difficult to increase the frame fixing strength of the resin member.
Moreover, a considerable height difference has to be made in the thick portion so as to make the frame protrude through the resin member on the back face thereof, and the flatness of the back face of the semiconductor laser device is degraded due to the smallness of the area of the thick portion. This impairs the stability of the semiconductor laser device when it is handled or set. Furthermore, in a case where the semiconductor laser device using a frame package is used, for example, in an optical pickup, the bottom face of the frame package is seldom or never brought into contact with a body of the optical pickup. This makes it impossible to fully achieve the thermal dissipation effect of the semiconductor laser device.
On the other hand, a semiconductor laser device using a frame package that can improve the thermal dissipation characteristics and the strength as well as the flatness of the back face thereof is disclosed in Patent Publication 2. FIGS. 6 and 7 are a perspective view and a front view, respectively, of the semiconductor laser device. FIG. 8 is a sectional view taken along line X-X′ of FIG. 7.
A semiconductor laser device 80 has a submount 83 placed and fixed on a top of a frame 82. A semiconductor laser element 84 is placed and fixed on a top of the submount 83. The frame 82 is formed of metal having high thermal conductivity and high electrical conductivity such as copper, iron, or an alloy thereof, and is in the form of a flat plate. The frame 82 is composed of a main frame 86 on which the semiconductor laser element 84 is to be mounted, and subframes 87 and 88 for wiring, each of which is independent of the main frame 86. The main frame 86 and the subframes 87 and 88 are integrated together with an insulating resin molded portion 85 into a frame package.
The main frame 86 includes an element placement portion 86a, a lead portion 86b, and wing portions 86c and 86d. The submount 83 is mounted on the element placement portion 86a. The lead portion 86b serves as a current path. The wing portions 86c and 86d are so formed as to protrude from opposite sides for thermal dissipation and positioning. The main frame 86 has a thick portion 86e and a thin portion 86f formed therein. The thick portion 86e is formed by increasing the thickness of a front part of the element placement portion 86a and front parts of the wing portions 86c and 86d, and the thin portion 86f is formed by reducing the thickness of rear parts of the wing portions 86c and 86d and the lead portion 86b. 
Like the lead portion 86b, the subframes 87 and 88 are so formed as to be thin. This makes it possible to easily perform fine processing of the lead portion 86b and the subframes 87 and 88 when the frame 82 is formed by metal stamping. This makes it possible to make the semiconductor laser device 80 compact by keeping a space between the lead portion 86b and the subframes 87 and 88 as narrow as possible.
The resin molded portion 85 is formed by insert molding in such a way as to sandwich the front and back faces of the frame 82. The resin molded portion 85 has, on a front face thereof, a laser beam emission window 85a from which laser light is emitted, and a U-shaped enclosure portion 85b having an open front. The enclosure portion 85b has, at front edges of both side portions thereof, tapered faces 85c. The tapered faces 85c permit smooth insertion of the semiconductor laser device 80 when it is placed in a predetermined position. The resin molded portion 85 has, on a back face thereof, a solid flat face 85d that covers the element placement portion 86a and has substantially the same outer shape (a hexagonal shape) as the enclosure portion 85b on the front face.
The element placement portion 86a of the main frame 86 disposed inside the enclosure portion 85b and the subframes 87 and 88 have front faces exposed to the outside because the resin molded portion 85 is not formed thereon. The semiconductor laser element 84 is placed and fixed on the exposed element placement portion 86a with the submount 83 interposed therebetween. Then, the semiconductor laser element 84 and the main frame 86, and the submount 83 and the subframes 87 and 88 are connected together by a wire (not shown).
The submount 83 is built as a light receiving element whose base material is Si. This makes it possible to monitor light emerging from a rear face of the semiconductor laser element 84. Instead of Si, it is possible to use, for example, ceramic having high thermal conductivity such as AlN, SiC, or Cu, or metal material. Moreover, the submount 83 is fixed to the element placement portion 86a by using solder such as Pb—Sn, Au—Sn, or Sn—Bi, Ag paste, or the like. The semiconductor laser element 84 is fixed to a predetermined position of the submount 83 by using solder such as Au—Sn or Pb—Sn, Ag paste, or the like.
The semiconductor laser device 80 using a frame package structured as described above has the semiconductor laser device 84 having an open front face, thereby offering enhanced thermal dissipation characteristics. Moreover, since the back face of the frame 82 is not exposed on the resin molded portion 85, it is possible to thicken the resin molded portion 85. This increases the strength of the semiconductor laser device 80. Furthermore, the semiconductor laser device 80 has the bottom face with improved flatness and has a wide plane of support, whereby it can be set with high stability.    Patent Publication 1: JP-A-H11-307871    Patent Publication 2: JP-A-2002-43679 ([0010] to [0022], FIG. 1, FIG. 2, FIG. 4)